The present invention relates generally to methods and apparatus for cleaning disks, and more specifically to a novel in-situ magnetron assisted DC plasma etching apparatus and method for cleaning magnetic recording disks.
Magnetic recording disks are well known in the art. Typical hard disk magnetic recording disks comprise a disk-shaped aluminum substrate having a lower, non-magnetic layer such as Ni--P, a chromium-containing intermediate layer, an upper ferromagnetic metal layer, and a carbon-based protective over coating.
In the known disk-shaped recording media which have a ferromagnetic metal film as the magnetic film, the substrates generally consist of aluminum or aluminum alloys. For the production of these thin-film magnetic disks, in a first step, the aluminum substrates are typically coated with a hard, non-magnetic amorphous (Ni--P) lower film or layer. The great hardness of the lower layer improves the tribological properties of the magnetic disks and makes it possible, in a subsequent surface treatment step, to obtain a defined surface roughness which is necessary for reproducible flight behavior of the head and prevents sticking of the head to the magnetic disk.
To ensure optimum adhesion of the intermediate chromium layer to the lower amorphous layer, the amorphous (Ni--P) layer is typically polished and/or textured. After this polishing/texturizing step, the surface of the lower amorphous film is typically cleaned using various mechanical and chemical cleaning methods to remove abraded material and residues of the abrasive. However, small traces of organic and inorganic contaminants, such as dust particles from the air, bacteria from the washing tanks, and polishing residue remain on the disks, leading to poor adhesion between the intermediate chromium layer and the Al/(Ni--P) substrate. The poor adhesion can lead to delamination of the chromium layer and, thus, failure of the disk.
Cleaning the disk surfaces using sputter etching techniques is desirable. Various entities have attempted to use both DC and RF glow discharge techniques to clean disk surfaces. However, none of these attempts have been particularly successful. The DC and RF glow discharge techniques known in the prior art have a tendency to negatively affect the magnetic properties of the disks. In particular, the prior art techniques generally require high pressure and bias voltage. High pressure means that more gas atoms are around the disk, so the particles/atoms sputtered off the disk surface are more likely to collide with a gas atom and be bounced back to the disk surface; so called back scattering effect. In addition, high gas pressure in the etching chamber slows down the overall process because it requires longer gas pumping time before the disk can be sent to the next processing step, thus adversely affecting the overall system throughout.
Moreover, high bias voltage can cause surface damage, stressed surface, and trapped gases on the disk, which can lead to changes in the overall magnetic properties of the etched disk.
Finally, the other prior art etching processes also involve using reactive gases such as Oxygen, which are effective in removing hydrocarbons on the disks but also leave an undesired oxidized metal disk surface.